Various precursors are used to form thin films and a variety of deposition techniques have been employed. Such techniques include reactive sputtering, ion-assisted deposition, sol-gel deposition, chemical vapor deposition (CVD) (also known as metalorganic CVD or MOCVD), and atomic layer deposition (ALD) (also known as atomic layer epitaxy). CVD and ALD processes are increasingly used as they have the advantages of enhanced compositional control, high film uniformity, and effective control of doping. Moreover, CVD and ALD processes provide excellent conformal step coverage on highly non-planar geometries associated with modern microelectronic devices.
CVD is a chemical process whereby precursors are used to form a thin film on a substrate surface. In a typical CVD process, the precursors are passed over the surface of a substrate (e.g., a wafer) in a low pressure or ambient pressure reaction chamber. The precursors react and/or decompose on the substrate surface creating a thin film of deposited material. Volatile by-products are removed by gas flow through the reaction chamber. The deposited film thickness can be difficult to control because it depends on coordination of many parameters such as temperature, pressure, gas flow volumes and uniformity, chemical depletion effects, and time.
ALD is also a method for the deposition of thin films. It is a self-limiting, sequential, unique film growth technique based on surface reactions that can provide precise thickness control and deposit conformal thin films of materials provided by precursors onto surfaces substrates of varying compositions. In ALD, the precursors are separated during the reaction. The first precursor is passed over the substrate surface producing a monolayer on the substrate surface. Any excess unreacted precursor is pumped out of the reaction chamber. A second precursor is then passed over the substrate surface and reacts with the first precursor, forming a second monolayer of film over the first-formed monolayer of film on the substrate surface. This cycle is repeated to create a film of desired thickness.
Thin films, and in particular thin metal-containing films, have a variety of important applications, such as in nanotechnology and the fabrication of semiconductor devices. Examples of such applications include high-refractive index optical coatings, corrosion-protection coatings, photocatalytic self-cleaning glass coatings, biocompatible coatings, dielectric capacitor layers and gate dielectric insulating films in field-effect transistors (FETs), capacitor electrodes, gate electrodes, adhesive diffusion barriers, and integrated circuits. Dielectric thin films are also used in microelectronics applications, such as the high-K dielectric oxide for dynamic random access memory (DRAM) applications and the ferroelectric perovskites used in infrared detectors and non-volatile ferroelectric random access memories (NV-FeRAMs). The continual decrease in the size of microelectronic components has increased the need for improved thin film technologies.
Technologies relating to the preparation of nickel-containing thin films (e.g., nickel metal, nickel oxide, nickel nitride) are of particular interest. For example, nickel-containing films have found numerous practical applications in areas such as catalysts, batteries, memory devices, displays, sensors, and nano- and microelectronics. In the case of electronic applications, commercial viable deposition methods using nickel-containing precursors having suitable properties including volatility, reactivity and stability are needed. However, there are a limited number of available nickel-containing compounds which possess such suitable properties. For example, while bis(allyl)nickel, (C3H5)2Ni, may have suitable volatility and reactivity, it is known to have very low thermal stability and will decompose above about 20° C. See, for example, Quisenberry, K., et al., J. Am. Chem. Soc. 2005, 127, 4376-4387 and Solomon, S., et al. Dalton Trans., 2010, 39, 2469-2483. Accordingly, there exists significant interest in the development of nickel complexes with performance characteristics which make them suitable for use as precursor materials in vapor deposition processes to prepare nickel-containing films. For example, nickel precursors with improved performance characteristics (e.g., thermal stabilities, vapor pressures, and deposition rates) are needed, as are methods of depositing thin films from such precursors.